Dynamic balancing of risks and rewards in a large herbivore: Further extending predator-prey concepts to road ecology.

Animal behaviour is shaped by the ability to identify risks and profitably balance the levels of risks encountered with the payoffs experienced. Anthropogenic disturbances like roads generate novel risks and opportunities that wildlife must accurately perceive and respond to. Basic concepts in predator-prey ecology are often used to understand responses of animals to roads (e.g. increased vigilance, selection for cover in their vicinity). However, prey often display complex behaviours such as modulating space use given varying risks and rewards, and it is unclear if such dynamic balancing is used by animals in the context of road crossings. We tested whether animals dynamically balance risks and rewards relative to roads using extensive field-based and GPS collar data from elk in Yoho National Park (British Columbia, Canada), where a major highway completely bisects their range during most of the year. We analysed elk behaviour by combining hidden Markov movement models with a step-selection function framework. Rewards were indexed by a dynamic map of available forage biomass, and risks were indexed by road crossings and traffic volumes. We found that elk generally selected intermediate and high forage biomass, and avoided crossing the road. Most of the time, elk modulated their behaviour given varying risks and rewards. When crossing the highway compared with not crossing, elk selected for greater forage biomass and this selection was stronger as the number of highway crossings increased. However, with traffic volume, elk only balanced foraging rewards when they crossed a single time during a travel sequence. Using a road ecology system, we empirically tested an important component of predator-prey ecology-the ability to dynamically modulate behaviour in response to varying levels of risks and rewards. Such a test articulates how decision-making processes that consider the spatiotemporal variation in risks and rewards allow animals to successfully and profitably navigate busy roads. Applying well-developed concepts in predator-prey theory helps understand how animals respond to anthropogenic disturbances and anticipate the adaptive capacity for individuals and populations to adjust to rapidly changing environments.

Le comportement animal est influencé par la capacité des animaux à identifier et minimiser les risques rencontrés, tout en maximisant les gains obtenus. Les perturbations anthropiques, telles que les routes, engendrent de nouveaux risques et opportunités pour la faune. Les concepts de l'écologie prédateur-proie sont fréquemment utilisés pour comprendre les réactions des animaux aux routes (e.g. vigilance accrue, choix de couvert à proximité des routes). Cependant, même s'il est connu que les proies ajustent fréquemment leur utilisation de l'espace de façon à minimiser les risques et maximiser les récompenses, il n'est pas clair si une telle optimisation est utilisée par les animaux lorsqu'ils traversent des routes. Ici, nous avons évalué comment les animaux ajustent leur sélection d'habitat par rapport aux routes en fonction des risques et des récompenses disponibles. Nous avons examiné cette question chez les wapitis du parc national Yoho (Colombie-Britannique, Canada), où une autoroute majeure divise complètement leur domaine vital pendant une majeure partie de l'année. À l'aide d'une analyse de sélection d'habitat à fine échelle, nous avons testé si les wapitis optimisent les risques liés aux traversées d'autoroute et les récompenses alimentaires obtenues lorsqu'ils se déplacent entre des zones d'alimentation. Les récompenses ont été estimées à l'aide d'une carte dynamique de la biomasse végétale disponible pour les wapitis, et les risques ont été estimés en fonction des traversées de route et du trafic automobile rencontré. Nos résultats indiquent que les wapitis sélectionnaient généralement des zones d'alimentation avec une biomasse intermédiaire à élevée, et évitaient de traverser l'autoroute. La plupart du temps, les wapitis ajustaient leur sélection d'habitat en fonction des risques et des récompenses. Les wapitis sélectionnaient des zones d'alimentation avec une biomasse plus élevée lorsqu'ils traversaient l'autoroute, comparé à lorsqu'ils ne traversaient pas. Ils optimisaient également la biomasse végétale obtenue en fonction du nombre de traversées de l'autoroute effectuées durant une séquence de déplacement. Cependant, les wapitis optimisaient uniquement les récompenses alimentaires avec le trafic automobile durant les séquences de déplacement avec une seule traversée. Nous avons testé empiriquement un élément essentiel de l'écologie prédateur-proie, soit la capacité d'ajuster de façon dynamique un comportement en réponse à des niveaux variables de risques et de récompenses, dans le contexte de l'écologie routière. Notre étude permet d'illustrer comment les processus décisionnels considérant à la fois les risques, les récompenses et leur variation spatiotemporelle, permettent aux animaux de naviguer de façon optimale les routes très fréquentées. L'utilisation de concepts bien établis de l'écologie prédateur-proie aide à comprendre comment les animaux réagissent aux perturbations anthropiques, et contribue à anticiper la capacité d'adaptation des individus et des populations face à des environnements en transformation rapide.

Behavioral responses of terrestrial mammals to COVID-19 lockdowns.

COVID-19 lockdowns in early 2020 reduced human mobility, providing an opportunity to disentangle its effects on animals from those of landscape modifications. Using GPS data, we compared movements and road avoidance of 2300 terrestrial mammals (43 species) during the lockdowns to the same period in 2019. Individual responses were variable with no change in average movements or road avoidance behavior, likely due to variable lockdown conditions. However, under strict lockdowns 10-day 95th percentile displacements increased by 73%, suggesting increased landscape permeability. Animals' 1-hour 95th percentile displacements declined by 12% and animals were 36% closer to roads in areas of high human footprint, indicating reduced avoidance during lockdowns. Overall, lockdowns rapidly altered some spatial behaviors, highlighting variable but substantial impacts of human mobility on wildlife worldwide.

Diet energy density estimated from isotopes in predator hair associated with survival, habitat, and population dynamics.

Sea ice loss is fundamentally altering the Arctic marine environment. Yet there is a paucity of data on the adaptability of food webs to ecosystem change, including predator-prey interactions. Polar bears (Ursus maritimus) are an important subsistence resource for Indigenous people and an apex predator that relies entirely on the under-ice food web to meet its energy needs. In this study, we assessed whether polar bears maintained dietary energy density by prey switching in response to spatiotemporal variation in prey availability. We compared the macronutrient composition of diets inferred from stable carbon and nitrogen isotopes in polar bear guard hair (primarily representing summer/fall diet) during periods when bears had low and high survival (2004-2016), between bears that summered on land versus pack ice, and between bears occupying different regions of the Alaskan and Canadian Beaufort Sea. Polar bears consumed diets with lower energy density during periods of low survival, suggesting that concurrent increased dietary proportions of beluga whales (Delphinapterus leucas) did not offset reduced proportions of ringed seals (Pusa hispida). Diets with the lowest energy density and proportions from ringed seal blubber were consumed by bears in the western Beaufort Sea (Alaska) during a period when polar bear abundance declined. Intake required to meet energy requirements of an average free-ranging adult female polar bear was 2.1 kg/day on diets consumed during years with high survival but rose to 3.0 kg/day when survival was low. Although bears that summered onshore in the Alaskan Beaufort Sea had higher-fat diets than bears that summered on the pack ice, access to the remains of subsistence-harvested bowhead whales (Balaena mysticetus) contributed little to improving diet energy density. Because most bears in this region remain with the sea ice year round, prey switching and consumption of whale carcasses onshore appear insufficient to augment diets when availability of their primary prey, ringed seals, is reduced. Our results show that a strong predator-prey relationship between polar bears and ringed seals continues in the Beaufort Sea. The method of estimating dietary blubber using predator hair, demonstrated here, provides a new metric to monitor predator-prey relationships that affect individual health and population demographics.

Managing Genetic Diversity and Extinction Risk for a Rare Plains Bison (Bison bison bison) Population.

Unfenced plains bison are rare and only occur in a small number of locations throughout Canada and the United States. We examined management guidelines for maintenance of genetic health and population persistence for a small and isolated population of plains bison that occupy the interface between a protected national park and private agricultural lands. To address genetic health concerns, we measured genetic diversity relative to other populations and assessed the potential effects of genetic augmentation. We then used individual-based population viability analyses (PVA) to determine the minimum abundance likely to prevent genetic diversity declines. We assessed this minimum relative to a proposed maximum social carrying capacity related to bison use of human agricultural lands. We also used the PVA to assess the probability of population persistence given the limiting factors of predation, hunting, and disease. Our results indicate that genetic augmentation will likely be required to achieve genetic diversity similar to that of other plains bison populations. We also found that a minimum population of 420 bison yields low probability of additional genetic loss while staying within society-based maxima. Population estimates based on aerial surveys indicated that the population has been below this minimum since 2007. Our PVA simulations indicate that current hunting practices will result in undesirable levels of population extinction risk and further declines in genetic variability. Our study demonstrates that PVA can be used to evaluate potential management scenarios as they relate to long-term genetic conservation and population persistence for rare species.

Chronic stress and body condition of wolf-killed prey in Prince Albert National Park, Saskatchewan.

Chronic stress and poor body condition can cause adverse physiological and behavioural responses and may make animals more vulnerable to predation. We examined hair cortisol concentration (HCC) and marrow lipid content, as bioindicators of chronic stress and body condition, respectively, of bison (Bison bison bison), moose (Alces alces) and white-tailed deer (Odocoileus virginianus) killed by wolves (Canis lupus) in Prince Albert National Park (PANP), Saskatchewan, Canada. The Sturgeon River plains bison population in PANP is one of only a few wild populations of plains bison in their historical range in Canada and has experienced a decline of around 50% since 2005. We expected wolf-killed bison to have elevated HCC compared to human-harvested bison and that there would be a negative relationship between HCC and marrow lipids among wolf-killed animals. We compared HCC between different mortality sources for bison (wolf-killed n = 20 or human-harvested n = 23) and found that HCC was significantly elevated in wolf-killed bison (¯ = 7.56 ± 1.35 pg/mg). We found that HCC, species, sex and snow depth were all significant predictor variables of marrow lipid content of bison (n = 14), moose (n = 11) and deer (n = 27). Bison displayed the strongest negative correlation between HCC and marrow lipid content (r2 = 0.31). Our results suggest that chronic stress and poor body condition make prey more vulnerable to predation by wolves. HCC and marrow lipid content can provide reliable indicators of the physiological response of animals to stressors and may provide information on expected predator success that can be used to predict predator population dynamics.

Collective decision-making promotes fitness loss in a fusion-fission society.

While collective decision-making is recognised as a significant contributor to fitness in social species, the opposite outcome is also logically possible. We show that collective movement decisions guided by individual bison sharing faulty information about habitat quality promoted the use of ecological traps. The frequent, but short-lived, associations of bison with different spatial knowledge led to a population-wide shift from avoidance to selection of agricultural patches over 9 years in and around Prince Albert National Park, Canada. Bison were more likely to travel to an agricultural patch for the first time by following conspecifics already familiar with agricultural patches. Annual adult mortality increased by 12% due to hunting of bison on agricultural lands. Maladaptive social behaviour accordingly was a major force that contributed to a ~50% population decline in less than a decade. In human-altered landscapes, social learning by group-living species can lead to fitness losses, particularly in fusion-fission societies.

Habitat-mediated timing of migration in polar bears: an individual perspective.

Migration phenology is largely determined by how animals respond to seasonal changes in environmental conditions. Our perception of the relationship between migratory behavior and environmental cues can vary depending on the spatial scale at which these interactions are measured. Understanding the behavioral mechanisms behind population-scale movements requires knowledge of how individuals respond to local cues. We show how time-to-event models can be used to predict what factors are associated with the timing of an individual's migratory behavior using data from GPS collared polar bears (Ursus maritimus) that move seasonally between sea ice and terrestrial habitats. We found the concentration of sea ice that bears experience at a local level, along with the duration of exposure to these conditions, was most associated with individual migration timing. Our results corroborate studies that assume thresholds of >50% sea ice concentration are necessary for suitable polar bear habitat; however, continued periods (e.g., days to weeks) of exposure to suboptimal ice concentrations during seasonal melting were required before the proportion of bears migrating to land increased substantially. Time-to-event models are advantageous for examining individual movement patterns because they account for the idea that animals make decisions based on an accumulation of knowledge from the landscapes they move through and not simply the environment they are exposed to at the time of a decision. Understanding the migration behavior of polar bears moving between terrestrial and marine habitat, at multiple spatiotemporal scales, will be a major aspect of quantifying observed and potential demographic responses to climate-induced environmental changes.

Bison distribution under conflicting foraging strategies: site fidelity vs. energy maximization.

Foraging strategies based on site fidelity and maximization of energy intake rate are two adaptive forces shaping animal behavior. Whereas these strategies can both be evolutionarily stable, they predict conflicting optimal behaviors when population abundance is in decline. In such a case, foragers employing an energy-maximizing strategy should reduce their use of low-quality patches as interference competition becomes less intense for high-quality patches. Foragers using a site fidelity strategy, however, should continue to use familiar patches. Because natural fluctuations in population abundance provide the only non-manipulative opportunity to evaluate adaptation to these evolutionary forces, few studies have examined these foraging strategies simultaneously. Using abundance and space use data from a free-ranging bison (Bison bison) population living in a meadow-forest matrix in Prince Albert National Park, Canada, we determined how individuals balance the trade-off between site fidelity and energy-maximizing patch choice strategies with respect to changes in population abundance. From 1996 to 2005, bison abundance increased from 225 to 475 and then decreased to 225 by 2013. During the period of population increase, population range size increased. This expansion involved the addition of relatively less profitable areas and patches, leading to a decrease in the mean expected profitability of the range. Yet, during the period of population decline, we detected neither a subsequent retraction in population range size nor an increase in mean expected profitability of the range. Further, patch selection models. during the population decline indicated that, as density decreased, bison portrayed stronger fidelity to previously visited meadows, but no increase in selection strength for profitable meadows. Our analysis reveals that an energy-maximizing patch choice strategy alone cannot explain the distribution ofindividuals and populations, and site fidelity is an important evolutionary force shaping animal distribution. Animals may not always forage in the richest patches available, as ecological theory would often predict, but their use of profitable patches is dependent on population dynamics and the strength of site fidelity. Our findings are likewise relevant to applied inquiries such as forecasting species range shifts and reducing human-wildlife conflicts.

Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics.

Understanding how seasonal environmental conditions affect the timing and distribution of synchronized animal movement patterns is a central issue in animal ecology. Migration, a behavioural adaptation to seasonal environmental fluctuations, is a fundamental part of the life history of numerous species. However, global climate change can alter the spatiotemporal distribution of resources and thus affect the seasonal movement patterns of migratory animals. We examined sea ice dynamics relative to migration patterns and seasonal geographical fidelity of an Arctic marine predator, the polar bear (Ursus maritimus). Polar bear movement patterns were quantified using satellite-linked telemetry data collected from collars deployed between 1991-1997 and 2004-2009. We showed that specific sea ice characteristics can predict the timing of seasonal polar bear migration on and off terrestrial refugia. In addition, fidelity to specific onshore regions during the ice-free period was predicted by the spatial pattern of sea ice break-up but not by the timing of break-up. The timing of migration showed a trend towards earlier arrival of polar bears on shore and later departure from land, which has been driven by climate-induced declines in the availability of sea ice. Changes to the timing of migration have resulted in polar bears spending progressively longer periods of time on land without access to sea ice and their marine mammal prey. The links between increased atmospheric temperatures, sea ice dynamics, and the migratory behaviour of an ice-dependent species emphasizes the importance of quantifying and monitoring relationships between migratory wildlife and environmental cues that may be altered by climate change.